Answer:
Just the mention of moss in the lawn can ignite a heated discussion. Despite what many gardeners think, moss does not crowd out or kill grass, it grows where grass struggles. Most of the questions concerning moss are how to get rid of it. To deal with moss, start by determining why it is growing in that place and find out if anything else will grow in those conditions. Moss does best where the soil is compacted, poorly drained and shady. It also likes soils that have either a very high or very low pH and soil that is nutritionally poor. To deal with the existing moss right now, you can either rake it out or use one of the products on the market that kill moss, keeping in mind that these are only temporary solution. Soil should be tested before applying lime, sulfur or any other amendment used to adjust soil pH. For a long term solution, you need to change the conditions that favor the moss.
An aeration and seeding might be a good place to start plus a soil test which just may suggest a sulfur treament but only if the lab results recommend it. Even with all that, if the ground is in a damp, shady area you may simply continue to get it.